Unveiling the Role of Electrostatic Forces on Attraction between Opposing Polyelectrolyte Brushes.

Electrostatic interaction and molecular excluded-volume effects are responsible for a plethora of nonintuitive phenomena in soft-matter systems, including local charge inversion and attraction between similar charges. In the current work, we study the surface forces and swelling behavior of opposing polyelectrolyte brushes using a classical density functional theory that accounts for electrostatic and excluded-volume correlations. We observe that the detachment pressure between similarly charged brushes is sensitive to salt concentration in both the osmotic and salted regimes and can be negative in the presence of multivalent counterions. A comparison of the theoretical results with the mean-field predictions unravels the role of correlation effects in determining the surface forces and brush structure. For systems containing multivalent counterions, the detachment pressure attains negative values at an intermediate brush-brush separation, and the attractive region in the pressure vs distance plot is magnified in terms of both the depth and width of attraction with increasing counterion valency. However, the interbrush attraction vanishes when the size-induced correlations are switched off. We also investigated the role of counterion size and polymer chain length on the detachment pressure. It is found that smaller counterions are more effective in neutralizing the polymer charge than bigger counterions, leading to a reduced interbrush repulsion and, in some cases, attraction between like-charged brushes at intermediate distances. Meanwhile, varying the chain length of the grafted polymers only shifts the location of the attraction basin, with little influence on the interaction strength. The theoretical predictions show qualitative agreement with experimental observations and offer valuable insights into the interaction between similarly charged polymer brushes in the presence of multivalent ions.

Single-chain simulation of Ising density functional theory for weak polyelectrolytes.

Conventional theories of weak polyelectrolytes are either computationally prohibitive to account for the multidimensional inhomogeneity of polymer ionization in a liquid environment or oversimplistic in describing the coupling effects of ion-explicit electrostatic interactions and long-range intrachain correlations. To bridge this gap, we implement the Ising density functional theory (iDFT) for ionizable polymer systems using the single-chain-in-mean-field algorithm. The single-chain-in-iDFT (sc-iDFT) shows significant improvements over conventional mean-field methods in describing segment-level dissociation equilibrium, specific ion effects, and long-range intrachain correlations. With an explicit consideration of the fluctuations of polymer configurations and the position-dependent ionization of individual polymer segments, sc-iDFT provides a faithful description of the structure and thermodynamic properties of inhomogeneous weak polyelectrolyte systems across multiple length scales.

Present-Day Crustal Velocity Field in Ecuador from cGPS Position Time Series.

The present study analyzes the GNSS time series obtained between the years 2017 and 2022 for the calculation of absolute and residual rates of Ecuador in 10 stations (ABEC, CUEC, ECEC, EPEC, FOEC, GZEC, MUEC, PLEC, RIOP, SEEC, TPC) of the continuous monitoring REGME network. Considering that the latest studies refer to periods 2012-2014 and Ecuador is located in an area of high seismic activity, it is important to update the GNSS rates. The RINEX data were provided by the Military Geographic Institute of Ecuador, the governing institution of geoinformation in that country; for processing, GipsyX scientific software was used with a PPP mode, considering 24 h sessions, and high precision was achieved. For the analysis of time series, the SARI platform was used. The series was modeled using a least-squares adjustment, which delivered the velocities for each station in the three local topocentric components. The results were contrasted with other studies, obtaining interesting conclusions as the presence of abnormal post-seismic rates stands out due to the high rate of seismic occurrence in Ecuador, and reaffirms the idea of a constant update of velocities for the Ecuadorian territory and the inclusion of the stochastic factor in the analysis of GNSS time series, since it can affect the ability to obtain the final GNSS velocities.

Thermodynamic non-ideality in charge regulation of weak polyelectrolytes.

Polymer ionization differs from that for their monomeric counterparts due to intramolecular correlations. Such effects are conventionally described in terms of the site-binding model that accounts for short-range interactions between neighboring sites. With an apparent equilibrium constant for each ionizable group and the nearest-neighbor energy as adjustable parameters, the site-binding method is useful to correlate experimental titration curves when the site-site interactions are insignificant at long ranges. This work aims to describe the electrostatic behavior of weak polyelectrolytes in aqueous solutions on the basis of the intrinsic equilibrium constants of the individual ionizable groups and solution conditions underlying the thermodynamic non-ideality. A molecular thermodynamic model is proposed for the protonation of weak polyelectrolytes by incorporating classical density functional theory into the site-binding model to account for the effects of the local ionic environment on both inter-chain and intra-chain correlations. By an extensive comparison of theoretical predictions with experimental titration curves, we demonstrate that the thermodynamic model is able to quantify the ionization behavior of weak polyelectrolytes over a broad range of molecular architectures and solution conditions.

Ising density functional theory for weak polyelectrolytes with strong coupling of ionization and intrachain correlations.

We report a theoretical framework for weak polyelectrolytes by combining the polymer density functional theory with the Ising model for charge regulation. The so-called Ising density functional theory provides an accurate description of the effects of polymer conformation on the ionization of individual segments and is able to account for both the intra- and interchain correlations due to the excluded-volume effects, chain connectivity, and electrostatic interactions. Theoretical predictions of the titration behavior and microscopic structure of ionizable polymers are found to be in excellent agreement with the experiment.

Modeling Surface Charge Regulation of Colloidal Particles in Aqueous Solutions.

Colloidal particles are mostly charged in an aqueous solution because of the protonation or deprotonation of ionizable groups on the surface. The surface charge density reflects a complex interplay of ion distributions within the electric double layer and the surface reaction equilibrium. In this work, we present a coarse-grained model to describe the charge regulation of various colloidal systems by an explicit consideration of the inhomogeneous ion distributions and surface reactions. With the primitive model for aqueous solutions and equilibrium constants for surface reactions as the inputs, the theoretical model is able to make quantitative predictions of the surface-charge densities and zeta potentials for diverse colloidal particles over a wide range of pH and ionic conditions. By accounting for the ionic size effects and electrostatic correlations, our model is applicable to systems with multivalent ions that exhibit charge inversion and provides a faithful description of the interfacial properties without evoking the empirical Stern capacitance or specific ion adsorptions.

Selective Charging Behavior in an Ionic Mixture Electrolyte-Supercapacitor System for Higher Energy and Power.

Ion-ion interactions in supercapacitor (SC) electrolytes are considered to have significant influence over the charging process and therefore the overall performance of the SC system. Current strategies used to weaken ionic interactions can enhance the power of SCs, but consequently, the energy density will decrease due to the increased distance between adjacent electrolyte ions at the electrode surface. Herein, we report on the simultaneous enhancement of the power and energy densities of a SC using an ionic mixture electrolyte with different types of ionic interactions. Two types of cations with stronger ionic interactions can be packed in a denser arrangement in mesopores to increase the capacitance, whereas only cations with weaker ionic interactions are allowed to enter micropores without sacrificing the power density. This unique selective charging behavior in different confined porous structure was investigated by solid-state nuclear magnetic resonance experiments and further confirmed theoretically by both density functional theory and molecular dynamics simulations. Our results offer a distinct insight into pairing ionic mixture electrolytes with materials with confined porous characteristics and further propose that it is possible to control the charging process resulting in comprehensive enhancements in SC performance.

Non-scaling behavior of electroosmotic flow in voltage-gated nanopores.

Ionic transport through nanopores is of fundamental importance for the design and development of nanofiltration membranes and novel electrochemical devices including supercapacitors, fuel cells and batteries. Recent experiments have shown an unusual variation of electrical conductance with the pore size and the electrolyte parameters that defies conventional scaling relations. Here ionic transport through voltage-gated nanopores was studied by using the classical density functional theory for ion distributions in combination with the Navier-Stokes equation for the electroosmotic flow. We identified a significant influence of the gating potential on the scaling behavior of the conductance with changes in the pore size and the salt concentration. For ion transport in narrow pores with a high gating voltage, the conductivity shows an oscillatory dependence on the pore size owing to the strong overlap of electric double layers.

A molecular theory for optimal blue energy extraction by electrical double layer expansion.

Electrical double layer expansion (CDLE) has been proposed as a promising alternative to reverse electrodialysis (RED) and pressure retarded osmosis (PRO) processes for extracting osmotic power generated by the salinity difference between freshwater and seawater. The performance of the CDLE process is sensitive to the configuration of porous electrodes and operation parameters for ion extraction and release cycles. In this work, we use a classical density functional theory (CDFT) to examine how the electrode pore size and charging/discharging potentials influence the thermodynamic efficiency of the CDLE cycle. The existence of an optimal charging potential that maximizes the energy output for a given pore configuration is predicted, which varies substantially with the pore size, especially when it is smaller than 2 nm. The thermodynamic efficiency is maximized when the electrode has a pore size about twice the ion diameter.

A Molecular Theory of Polypeptide Adsorption at Inorganic Surfaces.

A faithful description of polypeptide adsorption at ionizable surfaces remains a theoretical challenge from a molecular perspective due to the strong coupling of local thermodynamic nonideality and ionizations of both the adsorbate and substrate that are sensitive to the solution condition such as pH, ion valence, and salt concentration. Building upon a recently developed coarse-grained model for natural amino acids in bulk electrolyte solutions, here we report a molecular theory applicable to polypeptide adsorption on ionizable inorganic surfaces over a broad range of inhomogeneous conditions. Our thermodynamic model is able to account for diverse solution effects as well as the amino-acid sequence on polypeptide adsorption and surface association such as hydrogen bonding or bidentate coordination. The theoretical predictions have been validated by extensive comparison with experimental data for the adsorption isotherms of three representative polypeptides at a titanium surface.

Universal approach for full endoscopic decompression and percutaneous transpedicular fixation of the lumbar spine: A medial central approach (ACM).

ABSTRACT: Cohort study.This study aimed to determine the effectiveness of the universal approach of full endoscopy and percutaneous transpedicular fixation via a medial central approach (ACM) performed to surgically treat patients with lumbar degenerative surgical pathologies.Alternatives to interventionist treatments available to patients with lumbar degenerative surgical pathologies are related to recovery from minimally invasive surgery. Considering this, full endoscopic spinal decompression (full endoscopy) and percutaneous transpedicular fixation via an ACM represent advances in neurosurgical procedures, in particular, spinal surgery. Thus, the introduction of endoscopic and minimally invasive surgeries for the lumbar region has become 1 of the most important advances in modern surgery.A cohort of 79 patients undergoing full endoscopy and percutaneous transpedicular fixation was evaluated 6 times in 1 year. Pain intensity was measured using the visual analog scale (VAS), and lumbar functionality was measured using the Oswestry Disability Index (ODI). Six evaluations were performed: before surgery and on discharge after surgery as well as at 1, 3, 6, and 12 months after surgery.Before the ACM was applied, the VAS pain score was 8.52. At 11 hours post-surgery, the pain score reduced to 2.59 points (a difference of 5.73 points; P = 0.001). Of the 10 ODI domains evaluated, a difference was found between the period prior to surgery and 1 month later (P < 0.01).The universal approach to full endoscopy and lumbar percutaneous transpedicular fixation via an ACM is highly effective for patients with lumbar surgical degenerative pathologies.

[Choice of and preference for home child-birth in Callao, Perú]. / Elección y preferencia del parto domiciliario en Callao, Perú.

OBJECTIVE: Identifying the personal factors and prenatal attention associated with choosing the home for giving birth. MATERIAL AND METHODS: The study included 52 cases (fertile women whose last childbirth had been at home) and 208 controls (fertile women residing in the same geographical area). The study was carried out in the Pachacútec micro-network. Analysis was both bivariate and multivariate. RESULTS: The cases' average age was 28 (6,5 SD) and 26 for controls (6,1 SD). Bivariate analysis demonstrated a significant association for different factors but these they were not confirmed when multivariate analysis was applied. The risk factors were the home as foreseen place for childbirth w = 34.8 (p = 0.0); OR = 31.7 (CI = 10.1; 99.8) and prenatal attention supplier w = 7.0 (p = 0.0); OR = 0.1 (CI = 0.0; 0.5). CONCLUSIONS: The home as foreseen place for childbirth and prenatal attention supplier were the factors which were highly associated with home childbirth.

El extracto etanólico de las flores de Laccopetalum giganteum (pacra-pacra) aumenta la fertilidad en ratas / Ethanolic flower extract from Laccopetalum giganteum (pacra-pacra) increases fertility in rats

Objetivos: Determinar si la administración por vía oral del extracto etanólico de flores de Laccopetalum giganteum (Pacra-pacra) en ratas normales aumenta la fertilidad. Diseño: Estudio experimental. Lugar: Facultad de Medicina y Facultad de Farmacia y Bioquímica, Universidad Nacional Mayor de San Marcos. Material biológico: Ratas. Intervenciones: Cuarentiocho animales fueron divididos aleatoriamente en 2 grandes grupos, de 24 cada uno. El primero fue control, con solución salina fisiológica (SSF) 5mL/kg y el segundo con extracto vía oral, 300 mg/kg, durante 15 días. Cada grupo consideró 6 hembras y 6 machos juntos, y 6 hembras y 6 machos separados. Los animales que estuvieron juntos fueron sacrificados, para observar la presencia de fetos en el útero; y a los animales que estuvieron separados, se les extrajo muestra de sangre, para conocer el nivel de testosterona en machos y LH, FSH, estrógenos y progesterona en hembras, expresándose en ug/dL; el dosaje hormonal se realizó por el método de electroquimioluminiscencia. Asimismo, se determinó GOT, GPT, urea y creatinina, según las técnicas utilizadas en el laboratorio clínico. Principales medidas de resultados: Gravidez, FSH, LH, estrógenos y progesterona en ratas hembras; testosterona en ratas machos. Resultados: Los flavonoides, compuestos fenólicos y taninos estuvieron en mayor cantidad en el extracto etanólico. El 100 por ciento de ratas que recibió el extracto etanólico de la planta y estuvo junto a los machos resultó grávida; y, las separadas que recibieron el mismo extracto, presentaron incremento de FSH en las hembras y testosterona en los machos, comparativamente a los controles respectivos. Los niveles de GOT, GPT, urea y creatinina se encontraron dentro de los límites aceptados. Conclusiones: En condiciones experimentales, el extracto etanólico de las flores de Laccopetalum giganteum (pacra pacra) incrementó la fertilidad en ratas normales.

Objective: To determine whether oral administration of the ethanolic flower extract from Laccopetalum giganteum (pacra-pacra) increases fertility in normal rats. Design: Experimental study. Setting: Faculty of Medicine and Faculty of Pharmacy and Biochemistry, Universidad Nacional Mayor de San Marcos. Biologic material: Rats. Interventions: Forty-eight rats were randomly distributed into 2 groups of 24 rats each. The first control group received solución salina fisiológica (SSF) 5 mL/kg and the second group 300 mg/kg of the extract, orally, for 15 days. Each group had 6 female rats and 6 male rats living together and 6 female rats and 6 male rats lived separate. The animals living together were sacrificed in order to observe the fetuses in the uterus. The animals that lived separate had blood samples taken in order to determine testosterone levels in male rats and LH, FSH, estrogen and progesterone levels in female rats using electro chemiluminescence. At the same time, liver function tests, urea and creatinine tests were done. Main outcome measures: Pregnancy, FSH, LH, estrogens and progesterone in female rats; testosterone in male rats. Results: Flavonoids, tannins and phenolic compounds were found in higher quantities in the ethanolic extract. All female rats receiving the plant extract and living together with the male rats got pregnant and the ones that lived separate had increased levels of FSH. Male rats had increased levels of testosterone as compared to the control group. Liver function tests, urea and creatinine were within acceptable limits. Conclusions: The ethanolic flower extract from Laccopetalum giganteum (pacra-pacra) increased fertility in normal rats.

Elección y preferencia del parto domiciliario en Callao, Perú / Choice of and preference for home child-birth in Callao, Perú

Objetivo: Identificar los factores personales y de la atención prenatal relacionados con la elección y preferencia domiciliaria del lugar del parto. Material y métodos El estudio incluyó a 52 casos: mujeres en edad fértil (MEF) cuyo último parto fue domiciliario; y 208 controles: MEF con parto institucional residentes en la misma área geográfica. El estudio se realizó en la Micro red Pachacútec (Callao-Perú). El análisis fue bivariado y multivariado. Resultados La edad promedio de los casos fue 28 años (DS=6,5), y de los controles fue 26 años (DS=6,1). El análisis bivariado demostró la asociación significativa de diversos factores pero al aplicar el análisis multivariado éstos no fueron confirmados. Finalmente, los factores de riesgo fueron: el domicilio como lugar previsto de parto w=34,8 (p=0,0); OR=31,7 (IC=10,1-99,8) y el proveedor de la atención prenatal w=7,0 (p=0,0); OR=0,1 (IC=0,0-0,5). Conclusiones El domicilio como lugar previsto de parto y el proveedor de la atención prenatal son los factores que están altamente asociados con el parto domiciliario.

Objective: Identifying the personal factors and prenatal attention associated with choosing the home for giving birth. Material and Methods The study included 52 cases (fertile women whose last childbirth had been at home) and 208 controls (fertile women residing in the same geographical area). The study was carried out in the Pachacútec micro-network. Analysis was both bivariate and multivariate. Results The cases' average age was 28 (6,5 SD) and 26 for controls (6,1 SD). Bivariate analysis demonstrated a significant association for different factors but these they were not confirmed when multivariate analysis was applied. The risk factors were the home as foreseen place for childbirth w=34,8 (p=0,0); OR=31,7 (CI=10,1;99,8) and prenatal attention supplier w=7,0 (p=0,0); OR=0,1 (CI=0,0;0,5). Conclusions The home as foreseen place for childbirth and prenatal attention supplier were the factors which were highly associated with home childbirth.